In this project we will examine the expression and regulation of the alpha1-antitrypsin (alpha1-AT) gene in the human enterocyte-like cell line, Caco2, as a model system for understanding mechanisms of enterocyte- specific gene expression. We have previously shown that the alpha1-AT gene is expressed in Caco2 cells and in human intestinal epithelial cells. Furthermore, expression of alphal-AT increases markedly during differentiation of Caco2 cells and in response to mediators of the inflammatory response, specifically interleukin-6. Preliminary results indicate that other serine proteinase inhibitors (serpins) are expressed in Caco2 cells in response to other mediators of the inflammatory response including interleukin-1, tumor necrosis factor and interferon-gamma. In fact these results indicate that changes in expression of several genes in Caco2 cells in response to cytokines are characteristic of the 'acute phase response.' The project will benefit from the extensive previous characterization of the structure and function of the target gene alpha1-AT, from previous characterization of the biochemistry and morphology of the Caco2 cell line and its differentiation in vitro, and from the availability of specific, physiologically relevant and highly purified regulatory proteins (interleukin-6, interleukin-1, tumor necrosis factor, interferon-gamma) First, we will identify transcriptional start sites, cis-acting DNA sequences and trans-acting DNA binding proteins responsible for increases in MI-AT gene expression during enterocyte differentiation. Second, we will compare the mechanism for increasing enterocyte alphal-AT gene expression during differentiation to that induced by cytokines. Third, we will determine whether the effects of differentiation and cytokines are specific for alpha1-AT or also apply to other proteinase inhibitors, integral membrane and cytosolic proteins of the enterocyte. We will also examine the contribution of local intestinal alpha1-AT gene expression to physiologic events in the intestine by detection of polymorphic variants of alpha1-AT in intestinal fluid after orthotopic liver transplantation. These studies will further define existing knowledge of mechanisms for enterocyte-specific gene expression. They will also provide information about mechanisms responsible for changes in gene expression during differentiation of enterocytes and during physiologic perturbations, such as those induced during the inflammatory response.